At present, the outboard engine market is dominated by petrol engines, which are mainly designed for smaller vessels, i.e. for the leisure market. Not only are petrol engines generally lighter than their diesel equivalents, conventional diesel engines for outboard motors often do not meet modern emissions standards. However, a range of users, from military operators to super-yacht owners begin to favour diesel outboard motors because of the improved safety of the heavier diesel fuel due to its lower volatility, and fuel compatibility with the mother ship. Furthermore, diesel is a more economical fuel source with a more readily accessible infrastructure.
In view of the above, diesel outboard motors have become the focus of marine research activity, with an aim to transforming the outboard engine market.
In order to fulfil current emissions standards, diesel internal combustion engines nowadays include more sophisticated charge systems. The new engines exhibit better performance, both in terms of power output and exhaust emission. In the past, charge performers utilised carburetors to fuel the combustion cylinders of the engine via manifold injection, whereas modern diesel engines use direct cylinder injection to improve performance characteristics. By injecting pressurised fuel directly into the combustion chambers, it is possible to achieve better air/fuel mixtures that result in better engine economy and emission control.
Particularly in vertical drive systems, e.g. for outboard motors, the utilisation of direct cylinder injection requires the use of high pressure pumps. Normally, positive displacement pumps are employed for this purpose. Some known drive systems include high pressure positive displacement pumps that are directly driven off the crankshaft of the engine.
Driving the fuel pump off the crankshaft comes with a number of issues. Firstly, due to the limited packaging space, it is generally undesirable to attach a high pressure fuel pump directly to the end of the crankshaft, resulting in bulkier arrangements. As a consequence, complicated transmission arrangements are often employed to place the high pressure pump within the existing space envelope.
In view of the above shortcomings of the prior art, it is an object of the present invention to overcome the problems associated with conventional solutions and provide a new drive system for outboard motors optimising the use of existing packaging space and exhibiting increased pump effectiveness.
According to a first aspect of the present invention, there is provided a drive system for a marine outboard motor, the drive system comprising an internal combustion engine connected to a proportion device, the internal combustion engine comprising a crankshaft for driving the proportion device, wherein, in use, the crankshaft is arranged to rotate about a substantially vertical crankshaft axis, and wherein the internal combustion engine further comprises a camshaft for operating one or more cylinder valves of the engine, said camshaft being arranged for rotation about a camshaft axis arranged substantially parallel to the crankshaft axis. The drive system further comprises a fuel pump for pressurising fuel used to operate the internal combustion engine, said fuel pump being configured to be driven by the camshaft.
Since drive systems for outboard motors usually include a vertical crankshaft, problems can occur with the orientation of the fuel pump if oriented in a standard orientation, with its axis of rotation parallel with a vertical crank shaft. In particular, the fuel pump is sensitive to the orientation in which it is operated, that is, high pressure fuel pumps are not designed to carry significant thrust loads along the pump rotational axis, such as when the pump axis is arranged vertically, i.e. in line with the crankshaft. The drive system of the invention seeks to address these drawbacks and others, as will be apparent from a full reading of the following specification.
In the specification, the fuel pump being “driven by the camshaft” means that the fuel pump is connected to the camshaft such that the hydraulic output of the fuel pump is directly dependent on the rotary speed of the camshaft. This particular arrangement has the advantage that existing packaging space can be used most effectively. Using the camshaft to drive the pump also eases maintenance of the drive system, since the pump can be arranged to be more readily accessible on the outside of the internal combustion engine. Where conventionally a fuel pump may have been driven directly from the crankshaft of an engine, in the present invention, although the drive ultimately is derived from the crank shaft, (as is all rotary power generated in an internal combustion engine of the type described herein), in the invention, the camshaft lies in the drive train between the crankshaft and the fuel pump.
In the present specification, the term “vertical” when applied to the combustion engines or shafts described herein, is intended to reflect the orientation of the relevant shafts during normal use of the engine. A skilled reader will therefore appreciate that, for example, a vertical crankshaft or cam shaft axis is one which is oriented in a substantially vertical direction during use of the engine. In a marine outboard motor this will be understood to mean that the relevant axis is substantially parallel to an axis passing from the power head to the lower section of the outboard motor, or otherwise substantially in line with the leg of the motor. Vertical is understood in the normal way, i.e. defined by the direction of gravity during normal use of the engine.
In another embodiment, the fuel pump comprises an input shaft arranged to rotate about an input shaft axis, said input shaft axis being arranged at an angle between 30 to 150 degrees with respect to said camshaft axis. The angle between the input shaft axis and the camshaft axis may preferably be in the range of 80 to 100 degrees. In one embodiment, the input shaft axis may be arranged substantially perpendicular to the camshaft axis. In a drive system of the present invention, the crankshaft and the camshaft are arranged in a vertical direction. Arranging the input shaft axis of the pump perpendicular to the camshaft axis, therefore, allows for the pump to be arranged in a substantially horizontal direction. This will cause the high pressure fuel pump to work more effectively, as the pump is not required to carry significant thrust loads along the pump rotational axis.
In another embodiment, the camshaft is a substantially hollow shaft. This will reduce the weight of the drive system and provides access points for a transmission assembly described in more detail below.
The fuel pump may be a high pressure fuel pump. As such, the fuel pump may be used to supply pressurised fuel at a pressure of 1000 to 3000 bar for injection into the combustion cylinders. The fuel pump may be a gear pump. Implementing a gear pump as the fuel pump has the advantage that rotational energy from the camshaft can be directly applied to a rotary input shaft of the pump.
According to yet another embodiment, the drive system comprises a transmission assembly configured to connect the camshaft to the input shaft of the fuel pump. If the input shaft axis of the fuel pump is arranged at an angle with respect to the camshaft axis, as described hereinbefore, the transmission assembly may be used to establish said angular connection and transfer power between the camshaft and the input shaft. The transmission assembly may be an integral part of the fuel pump. Alternatively, the transmission assembly may be a separate part that is removably connected between the camshaft and the fuel pump. The transmission assembly may comprise gears to convert the rotational energy of the camshaft into the required input speed and torque for the input shaft of the fuel pump.
The camshaft may be connected to the transmission assembly such that the camshaft is movable along the camshaft axis with respect to the transmission assembly. In the vertical arrangement of the present drive system, the camshaft of this embodiment is movable upwards and downwards along its vertical camshaft axis whilst maintaining its connection to the fuel pump via the transmission assembly. The arrangement enables torque to be transferred from the camshaft to the fuel pump whilst permitting movement of the shaft along it rotational axis. In other words, the camshaft is floatingly connected to the transmission assembly. In one embodiment, the camshaft may, therefore, comprise a plurality of splines at a first end. The first end is connected to the fuel pump and, preferably, arranged at a bottom end of the camshaft. The splines may be arranged on an inner or outer surface of the camshaft and adapted to connect with a corresponding, splined part of the transmission assembly.
The transmission assembly may comprise a casing, releasably connected to a housing of the fuel pump. As such, the transmission assembly is easily removable from the fuel pump for maintenance purposes. The casing may also form an internal cavity configured to receive the lubricant. The casing may comprise an inlet port connected to an oil pump of the internal combustion engine. Consequently, the transmission assembly may be provided with lubricant by means of the existing lubrication system and does not require additional oil reservoirs to be provided.
In another embodiment, the transmission assembly comprises first and second bevel gears. The first and second bevel gears are arranged inside the internal cavity of the casing, which simultaneously acts as a lubrication chamber for the latter. The bevel gears are adapted to connect the camshaft and the input shaft of the fuel pump at the desired angle, e.g. 90 degrees. The first and second bevel gears may include straight or helical teeth, which are in meshing engagement to transfer the rotational energy of the camshaft to the input shaft of the fuel pump.
The first and second bevel gears may have an integer gear ratio. Alternatively, the first and second bevel gears may have a non-integer gear ratio.
In another embodiment, the transmission assembly may comprise a constant-velocity joint. In yet another embodiment, the transmission assembly may comprise a universal joint.
The internal combustion engine may comprise first and second cylinder bank arranged in a V-shaped engine block having a valley defined between a first plane extending through the first cylinder bank and a second plane extending through the second cylinder bank, wherein the fuel pump is arranged within said valley. Arranging the fuel pump within the valley, between at least the planes of the first and second cylinder banks, and optionally between the cylinder banks themselves, optimises the use of the available packaging space within the cowling of an outboard motor.
The valley of the V-shaped engine block may comprise a first end arranged closer to the propulsion device than an opposite, second end, wherein the fuel pump may be arranged at or toward the first end of the valley. In other words, the fuel pump may be arranged at or toward a bottom end of the valley. This arrangement supports the connection between the camshaft and the input shaft of the fuel pump via the transmission assembly, as the camshaft may simply protrude from its corresponding valve block at the bottom end thereof.
According to yet another embodiment, the drive system comprises a cowling surrounding the internal combustion engine and the fuel pump. A fuel rail may be received within the cowling and may be hydraulically connected to an outlet port of the fuel pump. Similar to the fuel pump, the injector rail may be arranged within the valley of the V-shaped engine block, or at least between the planes of the first and second cylinder banks.
In another embodiment, the propulsion device may comprise a propeller arranged to rotate about a propeller axis, wherein the propeller axis is substantially perpendicular to the crankshaft axis.
In another aspect of the present invention, there is provided an outboard motor for a marine vessel comprising the drive system described hereinbefore.
In yet another aspect of the present invention, there is provided a marine vessel comprising the outboard motor.
Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim even if not originally claimed in that manner.